In cancer treatment in recent years, a particle beam therapy method is widely used. In the particle beam therapy method, a cancer lesion area is irradiated with a particle beam that is generated by accelerating charged particles such as protons and carbon ions to high energy.
In the particle beam therapy method, in order to irradiate a cancer lesion area with a particle beam without irradiating important organs, it is required to perform irradiation changing the irradiation angle of the beam variously. Thus, for instance, a particle beam irradiator is fixed to a cylindrical rotating gantry to rotate together, thereby is changed its irradiation angle.
The inner space of the rotating gantry serving as a treatment room is provided with a movable floor that maintains a flat horizontal floor surface regardless of the rotation of the rotating gantry.
By using the movable floor, a technician accesses a patient before and after treatment and the patient comes down from the treatment table in case of emergency.
In order not to hinder the displacement of a tip portion of a particle beam irradiator which is fixed to the treatment room to protrude its tip portion into the treatment room, the movable floor slides in accordance with the displacement of the tip portion.
Before or during the irradiation of the particle beam, X-ray imaging is performed so that the position and shape of the lesion area are accurately analyzed.
Thus, an X-ray generator for radiating X-rays toward the patient and an X-ray detector for detecting X-rays transmitted through the patient (hereinafter, both are referred to as “X-ray imaging devices”) are arranged in the treatment space.
Since a particle beam therapy apparatus is equipped with some devices that change their relative positions as described above, it is necessary to consider the changes of the relative arrangements of the X-ray imaging devices.
For instance, there is a known method of connecting arms with the X-ray imaging devices and storing the arms together with the X-ray imaging devices at a place that the arms and the X-ray imaging devices do not collide with any other device in the treatment room.
In this case, the arms being controlled so as not to hinder the replacements of other devices, the X-ray generator is placed in the vicinity of the lesion area only at the time of X-ray irradiation, and after the completion of imaging, the X-ray generators are retracted.
However, the above-described technique has a problem that the arms and their control mechanisms complicate the particle beam therapy apparatus and the treatment time is prolonged by the arrangement time and retraction time of the X-ray imaging devices.
Nevertheless, X-ray images acquired by X-ray imaging are required to be clear to the extent that the position of the lesion area can be accurately specified.